Piezoelectric apparatus



Aug 9, 1938.

A. L. W. WILLIAMS PIEZOELECTRIC APPARATUS v Original Filed April 14, 1934 BY A INVENTQR.

ATTORNEY.

. re gned Aug.9, 193s 4 8.-

UNITED STATES PATENT OFFICE IPIEZOELECTRIC APPARATUS Alfred L. W. Williams, Cleveland Heights, Ohio, assignor to The Brush Development Company, Cleveland, Ohio, a corporation of Ohio Original application April 14, 1934, Serial No. 720,593. Divided and this application August 9,1937, Serial No. 158,044

7 Claims. (Cl. 171-327) This invention relates to piezo-electric devices thin paper, which are cemented to the faces of for conversion of mechanical into electrical enthe crystal units and to the top and bottom faces ergy or vice versa, and particularly to such deof the supports 2. vices employing crystal of the flexing type, 'As best shown in Figs. 4 and 5, each crystal 5 such, for example, as are disclosed in United unit consists of two plate-like elementsfl and 5, 5 States Letters Patent Reissue No. 20,680 and the plate 4 having metal foil electrodes 6 and I Reissue No. 20,213. The present application is a cemented on its outer and inner faces, respecdivision of my copending application Serial No. tively, and the plate 5 having electrodes 8 and 9 720,593, filed April 14, 1934. cemented. on its outer and inner faces, respec- 10 One object of the invention is to provide an tively. T e two plates thus formed are cemented 10 improved piezo-electric device of the type in together and leads ID and II are brought out which the flexible crystal unit acts as a diafrom the outer and inner electrodes, respecphragm to coact with the surrounding medium tively. The crystal plates 4 and 5 are formed and in which an improved type of support. is parallel to the plane of the b and c axes of the provided for the crystal unit or units. crystal with the sides or edges of the plates dis- 15 Another object of the invention is to provide posed at 45 degrees to said b and c axes. Thus an improved piezo-electric microphone having the it will be seen that the crystal units are supadvantages of faithful and non-directional reported by the microphone frame or support at sponse, insensitiveness to mechanical shock, relatwo points at the opposite ends of an axis of tively small size and light weight, and simple and expansion and contraction. 0 rugged construction. In the operation of the microphone sound 'Other objects of ,the invention, more or less waves orother mechanical impulses in the surincidental or ancillary tb the other objects rounding medium'acting upon the sides of the stated, will appear from the following specificamicrophone result in a flexing of the crystal units 2 tion describing a preferred embodiment of the with resultant generation of electromotive forces invention. at their electrodes and such electromotive forces In the drawing, may be conducted away to actuate loudspeakers Fig. 1 is an enlarged plan view of a microor to perform other functions.

phone embodying my improvements. In practice it is convenient to connect leads Fig, 2 is an nlarged side 91' edge elevation of IO, I0 together and leads II, II together, each 30 the microphone. junction constituting one terminal of the unit.

Fig. 3 is a section on the line 33 of Fig. 1. The units may, however, as will readily be under- Fig. 4 is an enlarged plan view of one of the stood, be connected in series. In'either case the crystal units of the microphone. units I, I must be so oriented that their electri- Fig. 5 is an enlarged side or edge elevation of cal impulses reinforce each other when the units 35 the said unit with the parts separated enough are simultaneously flexed toward or away from to show more clearly the construction. each other by fluid mediumirnpulses. V Fig. 6 is a diagram showing in enlarged per-' The paper sheets 3, 3, together with frame 2, spective the crystal units of the microphone and shield the inner faces of the crystal units, thus 40 illustrating the manner in which the units flex effectively preventing the mechanical impulses of 40 in operation. the surrounding medium from acting on the in- Referring in detail to the construction illusner faces. trated in the drawing, a pair of crystal units With the crystal units I, I locally supported I, I are mounted in parallel spaced relation in by the lugs 2a, 2a, impulses or pressure variaa frame-like support designated in its entirety tions of the fluid medium surrounding the micro- 45 by 2. This support is preferably formed of a phone cause the crystal units to flex in a double material such as Bakelite and is provided with curvature or what may be termed saddle form." two inwardly projecting lugs 2a, 2:1 for the sup'- This double curvature is illustrated in exagport of the crystal units I, I. The frame can erated form in Fig. 6, which is an enlarged I 59 conveniently be formed in three parts, as shown diagrammatic representation of the crystal units in Fig. 3 by stamping the parts from sheet ma- I, I, and the lugs 2a, 2a, the remainder of the terial, the middle part being formed with the frame 2 and the paper sheets 3, 3 omitted. The

" lugs 2a, 2a. The two crystal units are secured crystal units are shown as flexed toward each in positionon the lugs by elastic cementat 2b other to indicate the efiect of an increase in and by sheets 3, 3 ofsuitable material, such as fluid medium pressure. This double curvature of the units, resulting from the application of distributed forces of the fluid medium on one face of each unit, sets up strains in the individual of the unit while all unsupported points of theother unit are similarly displaced in the opposite direction.

Thus it can be seen that by my invention I have provided apiezo-electric device for converting mechanical impulses of a fluid medium into elec trical impulses, and vice versa, which takes maximum advantage of the piezo-electric action of flexing crystal units composed of Rochelle salt or similar crystalline material.

Due to the efficient use of the piezo-electric action of flexing plate units as above described it is possible to make microphone units of very small size thus reducing the eifect of pressure doubling, phase shift, and diaphragm resonance usually encountered in other types of construction. For this reason and because the microphone is a pressure-sensitive device'it has very faithful and substantially non-directional response over awide range of frequencies. For example, a highly satisfactory microphone may be constructed as shown in Figs. 1, 2 and 3 by making the crystal units I, I approximately square by 0.030" thick and the remainder of the parts in proportion.

' structed has substantially uniform response, on

' tion I have provided a microphone that is rela-' tively insensitive to mechanical-vibrations of the open circuit, for frequencies from below audibility to approximately 10,000 cycles with somewhat increased response at higher frequencies reaching a peak at the mechanical resonance of the crystal unit inthe neighborhood of 17,000 cycles. Obviously by changing the length, width and thickness of the crystal units the response characteristics can be altered to suit a variety of conditions.

Since the crystal units I, I are so oriented that their electrical impulses combine in additive relation when they are flexed toward or away from each other (under the influence of pressure impulses in the surrounding medium), impulses applied to the units as the result of mechanical vibrations of the frame 2 cause the unit to flex practically simultaneously in the same direction with resultant subtraction-of their individual impulses. Thus it will be evident that by my invenframe such as might be imparted by mechanical shock. I

It will be understood that my invention is not limited to the specific form of construction herein illustrated and described and that various features of the invention may take various other forms within the scope of the appended claims.

What I claim is: v

1. A piezo-electric device having a flexing type piezo-electric unit, supports for said unit disposed substantially at the ends of an axis of expansion and contraction of said unit and adapted to prevent motion of adjacent portions of said unit normal to the faces of said unit, and means connected to the edges of said unit adapted to shield A microphone so co'n-\ "are disposed in substantially parallel spaced reone of its faces from the surrounding fluid medium and adapted to permit vibratory motion of the unsupported portions of said unit substantially normal to its faces.

2. A piezo-electric device having a cell-like structure comprising a crystal unit which has a plurality of parallel plates of crystalline material with two mutually intersecting major axes of expansion and contraction, the faces of the plates being substantially parallel to the said axes and said unit being adapted to flex under the influence of electrostatic fields; supporting means for the unit disposed to engage it at the two ends of one of the two said major axes to prevent substantial movement of the adjacent parts of the unit normal to its faces while permitting such movement -of other parts of the unit; and means serving, in conjunction with the said unit, substantially to enclose'a spaceadjacent the inner face of the crystal unit.

3. A piezo-electric, device having a cell-like structure comprising a plurality of crystal units, each of which has a plurality of plates of crystalline material with two mutually intersecting major axes of expansion and contraction, the faces of the plates being substantially parallel to the said axes and said units being adapted to flex under the influence of electrostatic fields; supporting means for each of the units disposed to engage it at the two ends of one of the two said major axes to prevent substantial movement of the adjacent parts of the unit normal to its faces while permitting such movement of other parts of the'unit; and means serving, in conjunction with the crystal units, to enclose a space adjacent the inner faces of said units.

4. A piezo-electric'device as in claim 3 in which there are two of the crystal units and said units lation to each other.

5. A piezo-electric device having a cell-like structure comprising a pair of crystal units each of which has a plurality of plates of crystalline material with two mutually intersecting major axes of expansion and contraction, the faces of the plates being substantially parallel to the said axes and said units being adapted to flexunder the influence of electrostatic fields; means engaging the units at the twoends of one of the two said major axes of each unit to space said 0 crystalline material with two mutually intersecting major axes of expansion and contraction, the faces of the plates being substantially parallel trfthe said axes and said unit being adapted to flex under the influence of electrostatic fields; a

rigid frame; supporting means for the crystal unit carried by the frame and disposed to engage the unit substantially at the two ends of one of the two said major axes to. prevent substantial movement of the adjacent parts of the unit normal to its faces while permitting such movement of 1 other parts of the unit; and flexible means joining the edges of the crystal unit to the frame and serving to prevent passage of the surrounding medium between the edges of the unit and the frame. x i

7. A piezo-electric device having a cell-like structure comprising a pair of crystal units each of which has a plurality of, plates of crystalline material with two mutually intersecting major axes of expansion and contraction, the faces of the plates being substantially parallel to the said axes and said units being adapted to flex under the influence of electrostatic fields; means enand means serving in conjunction with the said units to enclose the space between the inner faces 'thereof, said means comprising a rigid frame structure and flexible means joining the edges of the crystal units to the frame structure and. serving to prevent passage of the surrounding medium between the edges of the units and the frame. ALFRED L. W. WEHAMS. 

